A sheet-supporting mechanism of this general kind is known from German Auslegeschrift 1611362, as a "slidable lattice grate table." As disclosed here, a plurality of sinuous spring bands, which stand vertically upright and support the supplied sheets, in the direction of sheet travel, are arranged as variable-length table surfaces within a side guide recess of the feed table.
A further sheet-supporting mechanism is known from EPO268693B1. Here, a plurality of displaceable receiving elements are arranged, in the region of the recess, transversely to the direction of sheet travel. The receiving elements, which act as leaf springs and are guided on rods, include leg regions and V-shaped or U-shaped connecting regions, which are arranged edgewise and are situated in the plane of the feed table surface. They are pre-tensioned and can be compressed whenever the side guide recess is reduced in size and are automatically re-set whenever the recess is enlarged.
A drawback of the foregoing arrangement is that, the linear deformation within the recess (for adjustment to sheet width or format) is always accompanied by a dimensional variation (linear deformation in width) in the spring bands in the direction of sheet travel. This leads to "irregularities" in respect to the sheet transport, since particularly in the case of thin print material or high press speeds, there is no guarantee of the sheet being securely supported. There is the further drawback that, due to the geometry of the spring construction, disturbances occur in sheet travel if the edges of the print material are roughly cut or deformed since, for example, the sheet edge gets caught in the spring bands.
In DE4 105 966 C1, a cover device endeavors to eliminate these drawbacks. As shown here, cover bars which are supported against springs, in the recess of the feed table, are arranged such that they are movable perpendicularly to the table surface. A sliding block acts on the cover bars from above and forces them into the recess against the spring force.
Although this solution improves the sheet-guidance, in that the cover bars do not give rise to any dimensional variation, it is nevertheless very complex. Dust and dirt cannot be carried away and, therefore, is able to accumulate between the cover bars. Since these cover bars completely cover the side guide recess, no additional means for the guidance or alignment of the sheets (such as a pneumatic mechanism) can be used to guide the sheet in this region.